1. Field of the Invention
This invention relates to an apparatus for determining the dryness of inked paper using laser light absorption technique for application in inkjet printers. The invention provides direct in-line feedback as to the effectiveness of the drying of the ink placed deposited upon paper or other media. This disclosure describes the associated laser system designs and the technologies employed in the determination of drying efficiency of inks and other liquids placed upon a media.
2. Background of the Art
High speed production inkjet printers print at speeds exceeding 300 pages per minute are cost efficient color printers for many high volume printing applications. Water based inks employed provide lower cost and are more environmentally friendly than other inks. However, the water-based ink may not dry fast enough before the paper is folded or printed on the reverse side, causing print or image quality. The drying of water based inks currently use near infrared (NIR) heating elements, comprised of heating lamps, which can dry water/glycol based inks by heating to vaporize the water and glycol components of the ink formulation. The drying of water-based inkjet ink applied to media by high speed continuous forms inkjet printers is an evolving post-processing product for the printing market. Currently no known method is employed to determine the efficiency of the drying system in real time within the inkjet printer. A method by which real time feedback of the performance of the printer drying system to the controller would be beneficial to the desired dryness of the inked media.
High speed production inkjet printers manufactured by Ricoh, Canon, Kodak, Xerox and others, use aqueous based inks in many of their products. Water is the largest component, by weight comprising as much as 60%. Other liquid components include glycol and other semi-volatiles. These liquid components spread out onto, and are absorbed into, the print media. The spreading function and absorption into the media is dependent upon the media composition. For example, plain uncoated paper, is absorbs the liquid more readily than a coated paper. Oko, Asaf, et. al (2010) “Imbibition of picoliter water droplets on coated inkjet papers”, NIP26 and Digital Fabrication 2010 Technical Proceedings, pp 475-478. describe the wetting of ink on plain and coated papers with spreading observed over 1 ms of time. K. Vikman, et. al. (2005) “Water Fastness of Ink Jet Prints on Modified Conventional Coatings, IS&T Volume 20, N0.2, April 2005, describe the analysis of various coated papers absorption of ink utilizing FTIR and Raman Spectrometry methods. T. Hartus, (1999), “Thermal Analysis of Ink-Substrate Interactions and Drying in Ink Jet Printing” Graphic Arts in Finland, 28 (1999)1, 3-10 describes TGA and DSC methods to evaluate papers with differing pulp content and the resultant absorption of inks into the papers and the evaporation energies of various inks. Eichhorn et. al, (2013), “Determination of Dryness of Water-based Inket Ink”, NIP29 Digital Printing Conference, September 2013, (proceedings yet to be published at time of patent application), describe FTIR and TGA analysis of wet and dried inked paper as a function of dryness determination after the inked paper had been exposed to a drying system.
Evaporation of the water and glycol at room temperature is too slow for high speed print applications, where the paper is either stacked or rolled up immediately after printing. Therefore drying of the paper within seconds of depositing the ink to the printed page is advantageous. For water based inks, current drying methods use Near Infrared (NIR) lamps that are positioned along the direction of movement of the printable substrate after the inkjet printing heads, to rapidly heat up the ink and media substrate to vaporize the water and glycol. The NIR lamps have light emission spectra at wavelengths from about 800 to 1100 nm (by way of non-limiting examples). One NIR system is manufactured by Adphos USA (Brookfield, Wis.) that employs multiple NIR heating units consisting of NIR lamps with “focusing” shields above and below the paper in the printer. While massive heat can be generated by NIR lamps, the absorption efficiency into water is very low in the NIR region and much heat is needed to effectively dry the ink sufficiently to avoid smearing or blocking (adherence between sheets caused by binding through the inks). The determination of the dryness of the heated surface is important to the efficiency of the drying system and assurance that smearing and blocking do not occur. An in-line immediate feedback system determining the moisture content within the inked media would be a beneficial component of the printer drying system, which this invention addresses.
High speed production inkjet printing is an expanding market technology. The drying of water-based inkjet ink applied to media by high speed continuous forms inkjet printers, is an evolving post-processing product for the printing market. The efficiency of the dryers to remove the water and glycols, and other semi-volatile components of the ink can be determined by laboratory analytical techniques. Analytical methods employed to determine the level of dryness of inkjet printed paper utilizing Thermal Gravimetric Analysis (TGA), Fourier Transform Infrared Spectrometry (FTIR) may yield baseline characterizations by which the invention described within is characterized against. Experimental testing FTIR and TGA methods are described here within, showing the ability to discern the level of dryness of a water-based inkjet printed paper sample. The methods provide effective tools for analysis of drying, and point to methods by which real time in-line printer feedback may be developed and characterized as those employed in the invention.